Rubin had been confirmed to speak at our D11 conference in May; you don’t do that when you’re easing your way out. In the time between giving wide-ranging comments on Google’s plans two weeks ago and dropping out of a speaking slot at SXSW this past weekend, something changed.

But that doesn’t mean Rubin wasn’t ready to move on; as Android grew, he had been frustrated with the large-scale operational work, and wanted to return to passion projects in robotics and home automation, said sources close to Rubin.

In their explanations of the move, both Rubin and Page referred to Rubin’s desire to “start a new chapter at Google,” with Rubin saying he is “an entrepreneur at heart.” Though there’s much speculation that he might join Google’s “moonshot” group Google X, our sources said that was not necessarily the case.

Android — which began life as an independent company Rubin co-founded in 2003 — is now a massive and growing force in mobile. Sure, some might grumble about the many forks and flavors, but the software powers more than 750 million devices from scores of different hardware makers.

Android accounted for 70 percent of global smartphone shipments in the fourth quarter of 2012, according to IDC.

That’s compared to Google’s other operating system, Chrome OS, which along with Google Apps and the Chrome browser is one of Pichai’s main projects. Chrome OS and Chromebooks have yet to catch on with mass consumers, with limited success in the education vertical so far.

Putting Pichai in charge of the far more successful Android seems a way for Page to ease redundancy and friction, a move that many consider long overdue. If Google is going to really do mobile right, it shouldn’t be placing two bets.

Google’s two operating systems do have much in common, and increasingly so. Initially the two shared little, with Chrome OS aimed at non-touch laptops and Android focused on the phone. Android had its own browser, too. More recently, though, Chrome has become the default browser on Android, Chrome OS is on both touchscreen and non-touch devices, and Android has moved from the phone to tablets, TVs and even a few clamshell devices.

Beyond assigning Pichai to lead Android with existing VP Engineering Hiroshi Lockheimer, Page has made other changes toward a cohesive mobile strategy. For instance, long-time AdWords product management director Nick Fox recently moved to work on mobile advertising projects at Android.

But as for Rubin, when you talk to people in the technology industry about leadership, they continually return to comparisons to Steve Jobs. So Wednesday was a big day for invoking the late Apple CEO.

“Andy is more like Steve Jobs in his leadership style — top down,” said Keval Desai, a former Google product management director on ads who is now a venture capitalist at InterWest Partners. “Sundar is more of a collaborative and low key leader, but very effective at achieving big results.”

Rubin had sparred with Amazon, Alibaba and other Android partners, and for some critics seemed to have a definition of “openness” that was consistent only in his own mind.

Said one former Google executive, “Everyone loves Andy, but his leadership style is not ‘Googley.'”

Meanwhile, Pichai has a history of working with partners on Google technology — back to his first gig at the company in 2004 doing toolbar distribution deals with computer makers and browsers. He also worked on Google’s antitrust efforts to make sure Google search was an option on Internet Explorer.

Still, there’s a touch of Jobs in both men — Pichai’s recent Chromebook Pixel launch was a highly stylized event to present an end-to-end Google-made device that clearly had designs on Apple.

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